1. Field of the Invention
The present invention relates to a lithographic apparatus and a device manufacturing method.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. The lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs), flat panel displays, and other devices involving fine structures. In a conventional lithographic apparatus, a patterning means, which is alternatively referred to as a mask or a reticle, can be used to generate a circuit pattern corresponding to an individual layer of the IC (or other device), and this pattern can be imaged onto a target portion (e.g., comprising part of one or several dies) on a substrate (e.g., a silicon wafer or glass plate) that has a layer of radiation-sensitive material (e.g., resist). Instead of a mask, the patterning means can comprise an array of individually controllable elements that generate the circuit pattern.
In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and scanners, in which each target portion is irradiated by scanning the pattern through the beam in a given direction (the “scanning” direction), while synchronously scanning the substrate parallel or anti-parallel to this direction.
It is known to use, as an array of individually controllable elements, an array of mirrors in a matrix arrangement. Each of the mirrors can be individually tilted about an axis by applying a suitable localized electric field or by employing piezo-electric actuation means. The mirrors are matrix-addressable, such that addressed mirrors will reflect an incoming radiation beam in a different direction to unaddressed mirrors. In this manner, the reflected beam is patterned according to the addressing pattern of the matrix-addressable mirrors. The matrix addressing can be performed using suitable electronic means. In order to manufacture ever-smaller devices using lithography, it is necessary to reduce the size of the individually controllable elements that generate the pattern. However, as the individually controllable elements decrease in size, the mechanical stress at the hinges that support the individually controllable elements increases. Accordingly, the lifetime of the hinges, and the lifetime of the array of individually controllable elements, decreases. Furthermore, the size of the actuation force required to position an individually controllable element at a required location can also increase.
Therefore, what is needed is a system and method that allows an array of individually controllable elements to be formed in which the size of the individually controllable elements can be reduced.